The ferroelectric memory using ferroelectric capacitors is known as a nonvolatile memory. The ferroelectric memory utilizes the hysteresis characteristics of a ferroelectric substance to store data. Oxidation resistant metals such as Pt or electrically conductive oxides such as IrOx and RuOx are used as material for the upper electrode of a ferroelectric capacitor.
A ferroelectric capacitor having a two-layered upper electrode structure in which the composition of the upper layer is closer to the stoichiometric composition than the lower layer has been proposed. This constitution is expected to improve the capacitor characteristics.
A ferroelectric capacitor, the upper electrode of which consists of two layers, i.e. a SrRuO3 layer and a Pt layer, has been proposed. The SrRuO3 layer serves to depress the fatigue of the ferroelectric film.
A ferroelectric capacitor, the upper electrode of which consists of two layers, i.e. a highly conducting layer and an amorphous iridium oxide layer, has been proposed. The highly conducting layer is made of crystalline iridium oxide, SrRuO3, or the like.
A ferroelectric capacitor, the upper electrode of which consists of three layers, i.e. a SrRuO3 film, an oxygen-rich iridium oxide film, and an IrO2 film, has been proposed.
[Patent Documents]    [Patent document 1] Japanese Unexamined Patent Publication No. 2002-324894    [Patent document 2] Japanese Unexamined Patent Publication No. HEI 11-195768    [Patent document 3] Japanese Unexamined Patent Publication No. 2002-261251    [Patent document 4] Japanese Unexamined Patent Publication No. 2009-94200